1. Field of the Invention
The present invention relates generally to field of optical communications systems. More specifically, the present invention discloses an optical transceiver using a corner cube reflector with a transmissive aperture, a receiver aligned with this aperture, and an optical switch to modulate the intensity of the reflected beam.
2. Statement of the Problem
A wide variety of optical communications systems are known in the prior art. However, these systems have typically suffered a number of shortcomings. Chief among these has been the need for gimbals and other pointing and tracking devices to maintain the necessary optical link between the transmitter and receiver. This adds substantial cost, complexity, and weight. Another major shortcoming has been the substantial power requirements needed to operate an optical transmitter that generates its own output beam. This tends to substantially limit the portability and/or range of optical transmitters.
It has long been known that corner cube reflectors (having three mutually perpendicular reflective surfaces) have the property of producing a reflected ray that is parallel to, but in the opposite direction from an incident ray, regardless of the direction of the incident ray within the field of view of the corner cube reflector. Klein & Furtak, Optics, p. 183 (Wiley, 2nd ed., 1986). This principle has been applied in the past to help solve the pointing and tracking problems associated with optical communications systems.
The prior art contains several examples of optical communications systems. A number of devices and processes have been invented in the past relating to use of corner cube reflectors in optical communications, including the following:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Cathey, et al. 4,063,083 Dec. 13, 1977 Lego 4,131,791 Dec. 26, 1978 Eichweber 4,143,263 March 6, 1979 Eichweber 4,662,003 Apr. 28, 1987 Elger 4,717,913 Jan. 5, 1988 Inoue 4,721,363 Jan. 26, 1988 Aoshima, et al. 4,864,222 Sept. 5, 1989 Meyzonnette, et al. 4,887,310 Dec. 12, 1989 ______________________________________
Cathey, et al., disclose an optical communications system using a series of light-coupled interfaces along the path of a light beam. Each interface assembly includes light sensitive and/or light emitting elements for extracting and/or adding information to the light beam.
Lego discloses a search-and-locate system. A search beacon of laser radiation is transmitted by the search station. The person to be located has a locator unit with a corner cube retro-reflector 30 and a separate photodiode 46. The corner cube retro-reflector 30 reflects a portion of the search beacon back to the search station where it is detected by a receiving apparatus. The locator unit includes a reflection control shutter 32 which enables a message to be transmitted to the search station by modulating the reflected beam. As shown in FIG. 6, the control shutter 32 can made implemented by means of a layer of material 86 which rotates the plane of polarization of the transmitted light. This layer of material is placed between two polarizing filters 88 and 90. The photodiode 46 and demodulator circuit 52 can be used to control the shutter 32 to reflectively respond only to a search beacon transmitting a predetermined code.
Eichweber (U.S. Pat. No. 4,143,263) discloses an optical transceiver system involving a retro-reflector 8, a separate photo-electric sensor 2, and an optical modulator 7. The optical modulator 7 unmasks the retro-reflector 8 to reflect the input light beam 1 back to its source if the input beam has a predetermined coding. The shutter can also be used to modulate the return beam to transmit data to the source. Subsequent U.S. Pat. No. 4,662,003 provides additional improvements to this basic system. However, once again, a separate photo-electric sensor 6 is used.
Elger discloses a data telemetry system. Each transponder has a set of PIN diodes for receiving signals, and a set of infrared emitting diodes for transmitting signals.
Inoue discloses a temperature control device for a liquid crystal optical shutter. The unit includes a light source 16, heaters 17 and 19, a liquid crystal optical shutter 18, a focussing lens 20, control substrates 21a and 21b, and temperature sensing thermistors 22 and 30. When a power switch is activated, the heater 19 is continuously energized until the temperature of the shutter 18 reaches a predetermined temperature.
Aoshima, et al., disclose a voltage detector made of an electro-optic material whose refractive index is changed by the voltage to be measured. An end portion of this material has a corner-cube shape.
Meyzonnette, et al., disclose a retro-reflective transceiver which operates by inducing a wavelength shift in the return beam. This shift is detected by the master transceiver in a heterodyne scheme. Data is encoded onto the return beam by means of a Bragg cell or an acousto-optic device.
3. Solution to the Problem
None of the prior art references uncovered in the search show an optical transceiver having a truncated corner cube reflector in which a portion of the incoming beam passes through the corner cube reflector to a receiver located behind the truncated apex, and a portion of the beam is reflected back to the source through an optical switch that permits information to be transmitted back to the source by modulating the intensity of the reflected beam.